Printed circuit board intergrated switch

ABSTRACT

Printed circuit board ( 1, 2, 3 ) comprising at least a first layer ( 13 ) on which a first stationary contact terminal ( 18 ) is formed and one or more second layers ( 9, 22 ) being spaced apart from the first layer ( 13 ) by at least one intermediate layer ( 10, 11, 12 ) is shown, whereby at least a portion ( 5 ) of said one or more second layers ( 11, 12 ) extend into a recess ( 26 ) formed by at least a discontinuity of the intermediate layers ( 10, 11, 12 ). The portion in the printed circuit board is flexible and has a second terminal ( 6 ). Which can be brought into contact with the first stationary terminal ( 20 ).

FIELD OF THE INVENTION

[0001] The present invention relates generally to a switch and moreparticularly to a high frequency, medium to high power, switch.

BACKGROUND OF THE INVENTION

[0002] Within the field of telecom apparatuses, such as base stationsfor mobile telephony and terminals for mobile datacom equipment there isa need for switches and relays that provide high isolation typicallyexceeding 80 dB.

[0003] Micro mechanical switches (MEMS) constitute a promisingtechnology for providing miniaturised switches on for instance Siliconsubstrates. This technology, however, still leaves something to bedesired concerning the required high isolation. The following documentsare examples of MEMS.

[0004] Prior art document U.S. Pat. No. 6,057,520 discloses anelectrostatic operated device comprising a substrate, an insulatinglayer, and a substrate electrode for providing repulsive forces and aninsulating layer. A movable electrode is of flexible material isdeposited on the planar surface such that a distal portion can curl awayfrom the planar surface. Two composite layers with different thermalcoefficients of expansion will also curl the electrode.

[0005] U.S. Pat. No. 6,124,650 shows a MEMS magnetic actuation devicecomprising a latchable cantilever on which a soft latchable magneticmember is placed and a plane coil for moving the cantilever. Both thecantilever and the coil are mounted on a thin field substrate. Thisdocument moreover mentions that thermal; magnetic and electrostatic MEMSrelays are known in the art.

[0006] U.S. Pat. No. 5,475,318 shows a micro-cantilever with anintegrated heating element comprising fist and second layers, such assilicon dioxide and aluminium, of different coefficients of thermalexpansion. The micro-cantilever has a tip, which is brought into contactwith a material for measuring friction during atomic force microscopy.

[0007] U.S. Pat. No. 6,100,477 shows a MEMS electrostatic RF switchhaving a membrane, which is attached, by respective flexure structures,in two opposite ends to a substrate.

[0008] U.S. Pat. No. 5,959,338 discloses an electrostatic relay mountedon a silicon wafer. The relay comprises an upper poly-silicon diaphragm,a central electrode and a lower poly-silicon diaphragm. A conductivedepression in the wafer and a conductive portion of the lower diagramwill make contact due to electrostatic forces.

[0009] WO9936948 discloses a micro-mechanical device manufactured on asilicon substrate. On the silicon substrate, silicon dioxide layers areformed for etching material and releasing meander shaped cantileverbeams. A top metal layer is sputtered on the silicon dioxide layer. Thetop metal layer extends to vertical sections on the cantilever beams.

SUMMARY OF THE INVENTION

[0010] The invention seeks to provide a switch offering high isolationand good power and high frequency handling, which can be manufacturedwith standard production tools.

[0011] This object has been accomplished by the subject matter definedby claim 1.

[0012] It is another object to provide a switch integrated in a printedcircuit board.

[0013] This object has been accomplished according to claim 2.

[0014] It is another object to provide a switch that is activated byforce impact.

[0015] This object has been accomplished by claim 3.

[0016] It is another object to provide an electrically activated switch.

[0017] This object has been achieved by claims 5 and 6.

[0018] It is another object to achieve an even more compact switch.

[0019] This object has been achieved by claims 8 and 9.

[0020] Further advantages will appear from the following detaileddescription of the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 shows a first embodiment of the invention,

[0022]FIG. 2 shows a second embodiment of the invention,

[0023]FIG. 3 shows a first embodiment of a flexible portion shown inFIGS. 1 and 2,

[0024]FIG. 4 shows a third embodiment of the invention,

[0025]FIG. 5 shows a flexible portion of FIG. 4,

[0026]FIG. 6 shows an alternative embodiment to FIG. 5,

[0027]FIG. 7 shows a fourth embodiment of the invention, and

[0028] FIGS. 8-16 shows process steps for manufacturing the flexibleportion.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0029] In FIG. 1, a switch being integrated in a printed circuit board 1has been shown.

[0030] The printed circuit board 1 has a first layer 13 on which a firststationary contact terminal 18 is formed. The first terminal isconnected to a first conductive strip layer 19 on the first layer 13.

[0031] One or more second layers 9, 22 are provided comprising forinstance a carrier laminate 9 of polyimide and a second conductive striplayer 22. The latter second layers are spaced apart from the first layer13 by at least one intermediate layer—preferably comprising a prepreglayer 10, a laminate layer 11, and a prepreg layer 12.

[0032] It should be understood that the conductive strip layers 19 and22 advantageously form part of conventional circuit board connections(not shown) to other optional components (not shown) on the printedcircuit board by appropriate patterns and via holes. For this purpose,additional conductive layers may be formed on for instance the laminate11.

[0033] A portion 5 of said one or more second layers 9, 22 extend into arecess 26 formed by a discontinuity of the intermediate layers 10, 11,12. The portion 5 in the printed circuit board is flexible and has asecond terminal 6, which can be brought into contact with the firststationary terminal 18. In FIG. 3, a cross section of the carrierlaminate 9 with the flexible portion 5 being outlined as tongue has beenshown.

[0034] Moreover, the printed circuit board has a bottom layer oflaminate 7 whereon a layer of prepreg 8 having a corresponding recess 26to the recess mentioned above. Hence, the flexible portion 5 is forminga tongue on a carrier substrate 9 that extend into the recess 26.

[0035] Preferably, the second terminal 6 is formed by an elevatedplatform for establishing a well-defined contact point. Likewise, thefirst terminal 18 is rendered elevated.

[0036] Alternatively, the first conductive strip layer is forming thefirst terminal 18 and/or the second conductive strip layer 22 is formingthe second terminal 6.

[0037] Magnetic material deposits 28 are provided near and on the sameside of the second terminal 6.

[0038] Opposite the first terminal 18, on the other side of the secondthe laminate layer 13, a solenoid 31 is mounted for attracting themagnetic material deposits 28 on the tongue 4 upon appliance of a directcurrent over a set of terminals (not shown) to the solenoid 31. Thereby,the flexible tongue 5 bends and the first terminal 18 and the secondterminal 6 connect.

[0039] As appears from FIG. 1, the switch is completely enclosed in theprinted circuit board. Advantageously, conductive layers (not shown) onthe external sides of laminates 7 and 13 may be provided for providingelectrical screening. Hence, a cost-effective relay, with electricalproperties similar to a coax relay, has been accomplished.

[0040] As appears from the above embodiment, the recess 26 is forming asealed enclosure. It is envisioned that the enclosure could serve toobtain a clean and particle free “contact” environment around the switchterminals ensuring obviating pollution of terminals and a correspondinglong operating life. The enclosure may contain air, a gas or vacuum.Even a liquid may be used.

[0041] Since the switch function is integrated in the carrier, theswitch may advantageously form part of a microwave transmission line,e.g. a strip-line circuit. In this case, the flexible portion 5 and therecess 26 are preferably dimensioned such that the characteristicimpedance of the transmission line remains unchanged over the switch.

[0042] In the following, an exemplary manner of manufacturing especiallythe flexible portion will be described.

[0043] In FIGS. 8-16, exemplary process steps for manufacturing thecentral flexible portion 5, corresponding to layers 7-13, have beenillustrated.

[0044] The carrier 9 may be formed of FR4—a laminate of polyimide, withcopper layers 22 and 32 on both sides—although other materials may beused. The polyimide layer may have a thickness of 50 μm and the copper athickness of 18 μm.

[0045] Initially, a photo-resist 33 is applied on the laminate 9. Anopening of for instance 1 mm is formed. This has been shown in FIG. 8.The carrier is electro-plated with copper whereby a bottom layer isdeposited in the opening on the copper layer 22. Subsequently, theopening is filled by chemical plating to the extent shown in FIG. 9.

[0046] After the photo-resist is removed, FIG. 10 a surface treatment ofgold and nickel depositing is applied, whereby the elevated terminal 6is formed.

[0047] A resist layer 34 is provided over the structure, FIG. 11.Patterns in the resist layers are removed, FIG. 12, and the tongue 5having an extension of about 2-5 mm is carved out by laser cutting orplasma etching. First, the copper layers are removed by chemicaletching, FIG. 13, then the polyimide layer 9 is removed by laser cuttingas indicated in FIG. 14.

[0048] The etch resist 34 is removed and the structure shown in FIG. 15appears.

[0049] Finally, polymer pasta containing magnetic material is printed bya silk screen process on the tongue 5 with subsequent low temperaturehardening for forming the magnetic deposits 28, confer FIG. 16. Thereby,the tongue shown in FIG. 1 is produced. The magnetic deposits may beformed as an area surrounding the terminal 6 or as dots.

[0050] The additional layers of FIG. 1, are manufactured by known steps,which involve stacking, non-flow heating of the prepreg layers 8 and 11and pressing the structure together with laminate 7 and laminate 11.Finally, the laminate 13 is attached to prepreg 12 and the abovestructure by non-flow heating and pressing.

[0051] The second laminate 13, of for instance FR4 with a copper layer,is exposed to the same treatment as above whereby the strip 19 is formedhaving the second elevated contact platform 20.

[0052] The magnetic coil may be constituted by means of additional PCBlayers, e.g. of prepreg 14 and polyamide 15, in which a central magneticcore 16 and coil windings 17 are integrated.

[0053] This solution has been shown on the FIG. 2 embodiment of theswitch 2, which has a basis similar to layers 7-13 of FIG. 1.

[0054] In the additional layers 14/15, which may have an extension of4-5 mm, coil pattern layers 17 are provided by photo resist techniquesand connected by copper plated via holes (not shown). In the centre ofthe coil pattern, a hole is drilled in the additional layers 14/15 inwhich magnetic polymer pasta is applied for forming a magnetic core 16for concentrating the magnetic field.

[0055] As appears from FIG. 2, a third contact terminal 20 connecting tolayer 32 is provided on the laminate 7. Moreover, a fourth terminal 21connecting to a fourth strip layer 35 on laminate 7 is provided.

[0056] Thereby the switch may provide electrical connection in its restposition. For instance, the second terminal 6 may be connected with thethird terminal 20 by a via (not shown).

[0057] Hence, a complete relay functionality has been integrated in theprinted circuit board.

[0058] Like the above embodiment, the switch 2 may advantageously formpart of a microwave transmission line, e.g. a strip-line. Where theflexible portion 5 is in contact with terminal 20 in its restingposition, the switch is advantageously dimensioned such that it forms acontinuation of the strip-line without any substantial change to thecharacteristic impedance. Moreover, the switch may constitute atermination, whereby the terminal 20 is connected to a resistance.

[0059] In FIG. 8, a printed circuit board having a switch is shownwherein the flexible portion is moved by force being exerted via amember 30, such as a tool or a part of another apparatus through anaperture 29 in the laminate 7.

[0060] One application for the above switch may for instance be in acircuit that is rarely activated by for instance a service technician,for test purposes, hence justifying a particular cost effective orcompact realisation. However, the suitable applications are deemedvirtually unlimited.

[0061] In FIGS. 4-6, further embodiments of the present invention havebeen shown.

[0062] The flexible portion may also be moved by exposing the flexibleportion to thermal expansion.

[0063] In FIGS. 4 and 5, the flexible portion 5 is outlined as a bridgeportion. On the flexible portion, a heat strip 27 having a given ohmicresistivity has been provided. By applying a current through the heatstrip 27, power is dissipated in the flexible portion leading to thecorresponding part of the flexible portion being heated, effecting arise of the flexible portion. After sufficient heating, the secondterminal 6 is brought into contact with the first terminal 18 and thestrip 19 is brought into communication with strip 22. By continuedheating, the terminals remain in contact.

[0064] As appears from FIG. 5, the heat strip 27 and the strip 22 aresymmetrical with regard to the flexible portion for obtaining a smoothnon twisted thermal expansion. A via 25 is provided for obtainingconnection to the strip 22.

[0065] An alternative to the above circuit is shown in FIG. 6, wherebythe switching circuit, in the embodiment of strip 22, forms part of theheating circuit. The current used for heating the flexible portion isprovided by a low or high pass filter formed by inductors 23 andcapacitors 24 and separated from the signal or power being switched overfirst and second terminals 6 and 18.

[0066] The above embodiment is highly compact allowing a high packagedensity.

Reference Signs

[0067]1 first printed circuit board with integrated switch

[0068]2 second printed circuit board with integrated switch

[0069]3 third printed circuit board with integrated switch

[0070]3 a first control circuit

[0071]3 b second control circuit

[0072]4 fourth printed circuit board

[0073]5 flexible portion

[0074]6 second terminal

[0075]7 laminate

[0076]8 prepreg

[0077]9 carrier laminate

[0078]10 prepreg

[0079]11 laminate

[0080]12 prepreg

[0081]13 laminate

[0082]14 prepreg

[0083]15 polyimide film

[0084]16 core

[0085]17 coil pattern

[0086]18 first terminal

[0087]19 first conductive strip layer

[0088]20 third terminal

[0089]21 fourth terminal

[0090]22 second conductive strip layer

[0091]23 inductor

[0092]24 capacitor

[0093]25 via

[0094]26 recess

[0095]27 heat strip

[0096]28 magnetic material

[0097]29 aperture

[0098]30 member

[0099]31 solenoid

[0100]32 third strip layer

[0101]33 photo resist

[0102]34 etch resist

[0103]35 fourth strip layer

1. Printed circuit board (1, 2, 3) comprising at least a first layer(13) on which a first stationary contact terminal (18) is formed and oneor more second layers (9, 22) being spaced apart from the first layer(13) by at least one intermediate layer (10, 11, 12), whereby at least aportion (5) of said one or more second layers (11, 12) extend into arecess (26) formed by at least a discontinuity of the intermediatelayers (10, 11, 12), said portion in the printed circuit board beingflexible and having a second terminal (6), which can be brought intocontact with the first stationary terminal (18).
 2. Printed circuitboard according to claim 1, wherein a first conductive strip layer (19)is connected with or is forming the first terminal (18) and/or a secondconductive strip layer (22) is connected with or is forming the secondterminal (6).
 3. Printed circuit board according to claim 1 or 2,wherein the flexible portion (5) is forming a tongue.
 4. Printed circuitboard according to claim 3, wherein the flexible portion is moved byforce being exerted via a member (30), such as a tool.
 5. Printedcircuit board according to claim 3, wherein the flexible portion ismoved by force being exerted via magnetic force being provided by a coil(17, 16, 31) being arranged in the vicinity of the flexible member, andwherein magnetic material (28) is arranged on the flexible portion (5).6. Printed circuit board according to claim 5, wherein the coil isformed by a solenoid component (31) mounted on the first layer (13). 7.Printed circuit board according to claim 5 or 6, wherein the coil isformed by additional-layers (14, 15) in which a coil pattern (17) isembedded, the additional layers forming part of the printed circuitboard.
 8. Printed circuit board according to claim 1 or 2, wherein theflexible portion is forming a bridge.
 9. Printed circuit board accordingto claim 8, wherein a heat circuit (22, 23, 24, 27) is provided on or inthe flexible portion for exposing the flexible portion to thermalexpansion when subject to an electrical current.
 10. Printed circuitboard according to claim 9, wherein the heat circuit is constituted by aseparate heat strip (27) being arranged on the flexible portion (5). 11.Printed circuit board according to claim 9, wherein heat is providedthrough the conductor leading current through the respective first andsecond terminals when brought together, the heat being provided via alow or high pass filter (23, 24).
 12. Printed circuit board according toany previous claim except claim 4, whereby the flexible portion (5) andthe terminals of the switch (6, 18, 20) are enclosed in the printedcircuit board (1, 2, 3).
 13. Printed circuit board according to anyprevious claim whereby at least one the conductive strip layers, theflexible portion (5) and the recess (26) form a strip-line.